Patents in solar energy and wind power experienced the biggest surge, while patents for fossil fuel technologies showed a more modest increase and patents related to technologies for nuclear power were flat.

It’s a worldwide trend, this patent binge, and the MIT study looked at more than 73,000 patents issued in more than 100 countries between 1970 and 2009. Japan had led the way with the most solar patents, followed by the US and China, though China in recent years, China is the clear energy patent leader.

Between 2004 and 2009, the number of solar patents issued annually grew 13 percent each year. The United States issued more than 1,000 patents for renewable energy technology in 2009, a leap from about 200 per year between 1975 and 2000.

At the same time, global investment in clean energy is plunging, according to a report by Bloomberg New Energy Finance (BNEF).

For the third quarter of 2013, Bloomberg notes $45.9 billion in clean energy investment—14% lower than the second quarter of this year and 20% lower than the third quarter of 2012.

The word in the corridors of Bloomberg is that we’re looking at the second consecutive year of a decline in investment in renewable energy and energy-smart technology.

When BNEF noted the drop in clean energy investment last year, it was not concerned and indeed found optimism in the fact that the drop wasn’t greater. This time around, however, the optimism isn’t as easy to find:

“After the slightly more promising second quarter, we now have a very disappointing third quarter figure for investment,” BNEF CEO Michael Liebreich said in a statement, noting that the “loss of momentum since 2011 is worrying.”

The cause of the decline in global investment in clean energy is found in policy uncertainty in Europe, the promise of cheap gas in and from the US, wind and solar investment leveling off in China and what appears to be a slowdown in the clean energy ambitions among the power houses.

Separately, a Citibank report predicts that renewable energy will account for more than 70% of worldwide investment in new power generation by 2025.

Of the nearly $10 trillion expected to be invested into the power sector over the next decade, Citibank projects that more than $2 trillion will be invested in wind, followed by $1.5 trillion in hydropower and $1.3 trillion in solar power.